Nowadays, motor vehicles are equipped as a rule with power steering systems. It is an object of the power steering system to reduce the steering force requirement, that is to say the torque which is to be applied by the driver for a change in driving direction. In known power steering systems, this takes place as a function of the engine speed, since the pump for the assisting hydraulic system is driven by the vehicle motor. Furthermore, it is known to drive the pumps by actuable electric motors, as a result of which speed-dependent steering force assistance is made possible. Here, the assisting action of a power steering system of this type decreases as the speed increases. At high speeds, the driver therefore has to introduce a greater moment via the steering wheel for a change in the steering lock than at low speeds. In systems of this type, the input moment is adapted, that is to say regulated, to the respective conditions.
Superposition steering systems are characterized in that a further angle can be superimposed by an actuator onto steering angles which are input by the driver. For instance, DE 101 60 313 A1 discloses a superposition gear mechanism for a superposition steering system. This superposition gear mechanism is arranged between an input shaft which is connected to the steering wheel and an output shaft which is connected to a steering gear. This superposition gear mechanism is assigned an adjusting motor, and together they form the actuator. This actuator has the disadvantage that it is arranged between an input shaft and an output shaft, with the result that additional installation space is required in the region of the steering column and therefore a special steering column is required.